DYNAMIC UPPER AIRWAY IMAGING DURING AWAKE RESPIRATION IN NORMAL SUBJECTS AND PATIENTS WITH SLEEP-DISORDERED BREATHING

The effects of respiration on upper airway caliber were studied using cine computed tomography (CT) in 15 normal subjects, 14 snorer/mildly apneic subjects, and 13 patients with obstructive sleep apnea. All sub jects were scanned in the supine position during awake nasal breathing . Eight-millimeter-thick axial slices were obtained at four anatomic l evels from the nasopharynx to the retroglossal region every 0.4 s duri ng a respiratory cycle. Tidal volume measured from an integrated pneum otachograph signal was correlated with slice acquisition during inspir ation and expiration to generate loops comparing upper airway area and tidal volume. In all three' subject groups and at all anatomic levels studied, there were significant dimensional changes in upper airway c aliber during the respiratory cycle. The major findings in this invest igation include: (1) the upper airway was significantly smaller in apn eic than normal subjects, especially at the retropalatal low and retro glossal anatomic levels; in apneic patients the airway had an anterior -posterior configuration unlike the normal airway, which had a horizon tal configuration with the major axis in the lateral direction; (2) in all three subject groups, little airway narrowing occurred in inspira tion, suggesting that the action of the upper airway dilator muscles b alanced the effects of negative intraluminal pressure. In apneic patie nts there was more enlargement of the airway in early inspiration, pre sumably reflecting increased upper airway muscle dilator activity; (3) in expiration, positive airway pressure resulted in expansion of the airway; this expansion was largest in the apneic patients, indicating that the apneic airway was more distensible than the normal airway; (4 ) at the end of expiration the upper airway narrowed significantly, es pecially in the apneic patients. Thus the airway in apneic patients ma y be heading toward a closed position at end-expiration.